In the past, computing devices used keyboards and mice as input devices. Such input devices work well, but require the user to learn the keypad or learn mouse operation. Also, such input devices are not as intuitive to use as many users would like.
More recently, some computer device provide touch sensitive display screens that allow user input. These interfaces may be more intuitive than previous interfaces. However, typically they suffer from the user's hands occluding the display screen. Also, touch sensitive screens are most practical for portable devices or other devices in which the display screen is near the user. However, some devices such as desktop computers have a display screen that is typically some distance from the user. It can be impractical for the user to reach out and touch such a display screen to provide user input.